JOHNSON, Presiding Judge.

Timothy Postell was tried by a jury on charges of shoplifting and aggravated assault. The jury found him guilty of shoplifting but was unable to reach a verdict on the aggravated assault charge. The trial court entered a judgment of conviction as to shoplifting and declared a mistrial as to aggravated assault.

1. In two enumerations, Postell claims the trial court erred in denying his motion for directed verdict of acquittal as to aggravated assault because the state did not prove the elements of the offense beyond a reasonable doubt.

Ordinarily neither the grant of a mistrial nor the denial of a motion for directed verdict of acquittal is directly appealable. See McCuen v. State, 191 Ga. App. 645 ( 382 S.E.2d 422) (1989); Phillips v. State, 153 Ga. App. 410 ( 265 S.E.2d 293) (1980). However, the issue raised in these enumerations is tied to a directly appealable judgment of conviction and is appealable pursuant to OCGA § 5-6-34 (d).

A motion for directed verdict of acquittal in a criminal case should be granted only when there is no conflict in the evidence and the evidence demands a verdict of acquittal as a matter of law; a challenge to the sufficiency of the evidence in connection with the denial of a directed verdict of acquittal is evaluated based on the standard set forth in Jackson v. Virginia, 443 U.S. 307 (99 SC 2781, 61 L.Ed.2d 560) (1979). King v. State, 230 Ga. App. 301, 305 (3) ( 496 S.E.2d 312) (1998). Viewed in the light most favorable to the prosecution, the evidence shows: A grocery store manager noticed Postell putting cartons of cigarettes into his pants. The manager and two other employees confronted him. Postell grabbed a 12-inch packaged knife from a display shelf, unwrapped it, and came toward the employees with the knife. Postell came within arm's reach of one of the employees, pointing the knife and making jabbing motions. The employees backed away from him. Postell fled from the store and was apprehended shortly thereafter. There was more than sufficient evidence to withstand Postell's motion for directed verdict. A rational trier of fact was authorized to find him guilty of aggravated assault beyond a reasonable doubt. See Jackson v. Virginia, supra; Slade v. State, 267 Ga. 868, 869 (1) ( 485 S.E.2d 726) (1997).

2. Postell contends the trial court permitted his character to be improperly injected into the trial. Specifically, he complains of a store employee's testimony that Postell was acting "unusual" and another employee's testimony that Postell "looked kind of suspicious." We do not agree that either remark impugned Postell's character. See generally Pettis v. State, 224 Ga. App. 77, 78-79 (2) ( 479 S.E.2d 460) (1996); Redd v. State, 222 Ga. App. 595 (2) ( 474 S.E.2d 651) (1996). Moreover, Postell made no objection to the testimony at trial and did not preserve the argument for review on appeal. Thomas v. State, 224 Ga. App. 816, 818 (4) ( 482 S.E.2d 472) (1997).

3. Postell claims the trial court erred in sentencing him as a recidivist because the state failed to show that his prior guilty pleas were made freely and voluntarily. When the state proffered at the sentencing hearing certified copies of Postell's three prior shoplifting convictions, Postell stated that "any pleas must be freely and voluntarily entered and it's the State's burden to show that they were so done." The trial judge replied that two of the pleas were taken in front him and the third was taken in front of another judge, and that the court always inquires into the voluntariness of pleas before taking them. On that basis, the trial court found that the pleas were freely and voluntarily given. Postell excepted to the ruling based on the lack of evidence showing the pleas were made freely and voluntarily.

"A plea of guilty that is invalid under Boykin [v. Alabama, 395 U.S. 238 ( 89 SC 1709, 23 L.Ed.2d 274) (1969)] may not be used to enhance punishment in a subsequent trial. . . . [O]nce the defendant raises the issue of intelligent and voluntary waiver with respect to prior guilty pleas, the burden is on the state to establish a valid waiver. . . . Presuming waiver from a silent record is impermissible." (Citations and punctuation omitted.) Pope v. State, 256 Ga. 195, 209-210 (17) ( 345 S.E.2d 831) (1986); see Dowdy v. State, 209 Ga. App. 95, 96 (3) ( 432 S.E.2d 827) (1993).

The copies of the plea documents show that Postell was represented by counsel, but the record is otherwise devoid of any evidence that the pleas were free and voluntary. Under these circumstances, the trial court erred in admitting the pleas in evidence over Postell's objection. See Pope, supra (plea documents showing defendant was represented by counsel not sufficient to show pleas intelligent and voluntary); Gadson v. State, 197 Ga. App. 315, 317 (4) ( 398 S.E.2d 409) (1990) (certified documents showing guilty pleas but not showing defendant was advised of rights do not satisfy state's burden of proving pleas freely and voluntarily made). Compare Jones v. State, 161 Ga. App. 620, 623 (4) ( 288 S.E.2d 795) (1982) (showing by state sufficient where guilty plea documents affirmatively stated defendant was represented by attorney in good standing and was advised by the court of constitutional rights); and compare Miller v. State, 214 Ga. App. 393, 394 (2) ( 448 S.E.2d 20) (1994) (record introduced on prior charge showed defendant entered plea freely and voluntarily). Accordingly, the sentence must be vacated and the case remanded for hearing on this issue and resentencing.

Judgment of conviction affirmed; sentence vacated and case remanded. Smith, J., and Senior Appellate Judge Harold R. Banke concur.

JOHNSON, Presiding Judge.

DECIDED AUGUST 10, 1998.